Our long-range goal is to understand the role of estrogen (E) in male reproduction. The objective of this application is to determine how E mediates epididymis (EP)-specific sperm disorders. The central hypothesis is that diethylstilbestrol [(DES), a potent E agonist], when given to adult rats at a certain dose and for a certain duration, disturbs sperm functions at the level of the EP, but without affecting sperm in the testis. This hypothesis is based upon our strong preliminary/published data that DES treatment at a rate of 8 ug/rat/day for 6 and/or 9 days adversely affected sperm numbers and sperm motility patterns in the EP, reduced fertility, and reduced plasma testosterone (T), but did not affect sperm production in the testis. The objective of this application will be accomplished by testing hypotheses that 1) DES-induced reduced fertility results from deficits in epididymal sperm functions and/or a compromise in sexual behavior and can be prevented by co-administering T or antiestrogen (ICI 182,780); 2) DES-induced decrease in epididymal sperm numbers results from an acceleration of sperm transport in the EP and can be prevented by co-administering T; and 3) DES-induced changes in sperm motility/fertility coincide with changes in androgen and/or estrogen receptor proteins and/or epididymal secretory proteins. Various parameters that will be tested in animals treated with DES, DES+T, DES+ICI, or oil will include i) sperm fertility by in vitro inseminating a fixed number of caudal epididymal sperm, ii) sexual behavior by pairing males with females, iii) rate of sperm transport by determining sperm transit time, iv) androgen and estrogen receptor proteins by immunocytochemistry and Western blotting, and v) epididymal secretory proteins by gel electrophoresis of in vitro-labeled radioactive proteins. This research is innovative because it takes advantage of our DES rat model that is ideal for isolating EP-specific sperm effects. It is our expectation that the above experimental approaches will identify causes that led to reductions in fertility, epididymal sperm numbers, and sperm motility as a consequence of E exposure. These results will be significant because they are expected to provide landmarks that can be used to assess actions of endocrine disrupters and to provide therapeutic and contraceptive interventions that can be targeted at the level of the EP.